Pulmonary infection with the fungal pathogen, Pneumocystis jirovecii, is a common and often fatal complication of HIV infection/AIDS. Emerging data suggest that Pneumocystis may also complicate lung diseases in non-HIV infected hosts including those with COPD and solid organ transplant recipients. The long-term goal of this project is to develop a vaccine against Pneumocystis. To that end, we have identified a novel vaccine candidate for Pneumocystis termed mini-kexin. We have shown DNA vaccination with mini-kexin followed by mucosal boosting generates robust pulmonary immune responses and provides protective efficacy against Pneumocystis challenge in mice. Furthermore, the use of CD40L as a molecular adjuvant allows for protective antibody responses in CD4+ T cell-deficient mice, a model the closely replicates the immunodeficiency and susceptibility to PCP in AIDS. Based on these data LSUHSC has filed a provisional patent and a PCT on mini-kexin as a PCP vaccine. This STTR under MiniVax will be used to perform further lead optimization and investigate immunogenicity of mini-Kexin in SIV-infected macaques. We hypothesize that prime/boost vaccination with mini-kexin will result in antigen specific antibody responses that are protective against PC challenge on the mouse and that co-administration of CD40L with mini-kexin vaccination will provide effective systemic and mucosal antibody responses in the setting of low peripheral CD4+ T-cells, using a simian model of AIDS. We will first perform lead optimization of the vaccine platform in mice and then conduct an immunogenicity trial in Rhesus macaques rendered immunodeficient by infection with SIV Mac251 to model vaccine efficiency in an HIV-infected cohort. Specific Aim 1 is to perform lead optimization and compare efficacy of systemic versus mucosal immunization in CD4-depleted mice. Specific Aim 2 is to conduct an immunogenicity study in non-human primates.